(a) Field
The subject matter disclosed generally relates to a system and method for detecting signal ingress interferences in a cable distribution network.
(b) Related Prior Art
Among the more difficult problems faced by the broadband cable industry are those caused by signal leakage and ingress interferences. These interferences are caused by improper or defective RF shielding of passive or active components connected to the coaxial network. When signal leakage is present, it could cause potential impairments to licensed over-the-air services. When ingress interference is present, it could cause potential impairments to cable television data services. Ingress interfering signals can be generated by electromagnetic interference (EMI), radio-frequency interference (RFI) or TV interference (TVI).
Ingress by over-the-air signals can come from many sources such as regulated radio transmitters, Amateur Radio and military users. In addition to these licensed operators, there are even more sources of radio energy or noise. FCC's Part 15 regulations govern license-free transmitters used in walkie-talkies, video games, garage door openers, modulators and other unlicensed low-power radio transmitters. Unintentional sources of noise include computer equipment, microprocessor circuits used in consumer electronics equipment, motors, neon signs, thermostats, the electrical power distribution system, etc.
When the shield integrity is compromised, in addition to the problems associated with signal leakage, ingress interference is primarily manifested as a disturbance that can affect the subscriber's TV analog/digital reception, High Speed Data (HSD) or Voice-over-IP (VoIP) services. The resultant service costs (or lost subscribers) represent a financial loss to the broadband cable operator.
One of the first methods for ingress detection in the 5-42 MHz return band involves utilizing a spectrum analyzer at the head-end connected to a return path test point. The process requires a head-end technician and a plant maintenance technician to disconnect specific portions of the plant to locate source of ingress.
More recent methods have automated this manual process by dedicating or switching return path test points to a network based RF monitoring system located at the head-end, which provides return node visibility to a Network Operation Center. All return nodes would be tested and monitored by a centralized Network Operation Center (NOC). Once ingress impairment is detected by the NOC, a system maintenance ticket is issued to plant maintenance crew. Troubleshooting ingress can now be a one-man operation since plant maintenance technicians have visibility on return nodes spectrum using a hand-held meter which receives its data information through a forward path carrier.
Once ingress impairment is detected on a specific return node, the technician needs to identify from which segment of the node the ingress impairment is generated. To do so, the technician needs to utilize the ‘divide and conquer’ approach. Starting at the node, return pads are either removed/switched in value from each feeder leg until ingress disappears. Once the feeder leg contributing to the ingress impairment is identified, the search is narrowed down to a distribution area.
The technician then moves on to the next active device and repeats the process until he identifies the plant section from which ingress is coming. It may take a few iterations before isolating the ingress to a single distribution leg. At this point of the process, the technician will have to either remove or switch components (coupler boards, tap/coupler plates) to pinpoint ingress source. Removal of these components could be service disruptive if operator is not using RF/AC bypass taps.
Several problems are associated with the detection methods described above. For instance, If the technician is not using RF/AC bypass taps when performing the repairs, all subscribers living in the distribution area under ingress troubleshooting could have their Digital TV, HSD and VoIP services interrupted.
The detection methods are also time consuming because it may take the NOC few hours to confirm that a problem exists at the head-end. It could also take hours for troubleshooting the distribution network before finalizing location of defective component. Finally, it could take days to isolate ingress in the field depending on whether the ingress impairment is intermittent or not.
Therefore, there is a need for a new method for detecting signal ingress interferences which is time efficient before starting to cause problems to customers.